Devices and methods related to deposited support structures

ABSTRACT

The present disclosure describes medical devices comprising a bio-corrodible stent member and a graft member. The bio-corrodible stent member can comprise a metal applied directly to the graft member via a vapor deposition process, such as a chemical or physical vapor deposition process.

FIELD

The present disclosure relates generally to implantable, bio-corrodibledevices and, more specifically, to medical devices comprisingbio-corrodible metal stent members formed on a graft member.

BACKGROUND

Implantable medical devices are frequently used to treat the anatomy ofpatients. Such devices can be permanently, semi-permanently, ortemporarily implanted in the anatomy to provide treatment to thepatient.

In many cases, the device may comprise one or more components that aredesigned to provide treatment for a sufficient period, then to corrodeand/or dissolve and be absorbed by or otherwise incorporated into thebody. For example, an implantable stent-graft may comprise a stentcomponent designed to be absorbed by or otherwise incorporated into thebody after providing reinforcement to a vessel for a sufficiently longtreatment period.

Accordingly, there is a need for medical devices that feature one ormore components that can be easily and safely absorbed or incorporatedby the body, in a predictable manner, after sufficiently long treatmenttime has elapsed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the disclosure and are incorporated in and constitute apart of this specification, illustrate embodiments of the disclosure,and together with the description, serve to explain the principles ofthe disclosure, wherein;

FIG. 1 illustrates a perspective view of a medical device in accordancewith the present disclosure;

FIG. 2 illustrates a method for forming a medical device in accordancewith the present disclosure; and

FIGS. 3A-3C illustrate various masks for use in forming a medical devicein accordance with the present disclosure.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Persons skilled in the art will readily appreciate that various aspectsof the present disclosure can be realized by any number of methods andsystems configured to perform the intended functions. Stateddifferently, other methods and systems can be incorporated herein toperform the intended functions. It should also be noted that theaccompanying drawing figures referred to herein are not all drawn toscale, but can be exaggerated to illustrate various aspects of thepresent disclosure, and in that regard, the drawing figures should notbe construed as limiting.

As used herein, “medical devices” can include, for example, stents,grafts, stent-grafts, filters, valves, occluders, fasteners, supports,sensors, markers, therapeutic agent delivery devices, and otherendoluminal and implantable devices that are implanted, acutely orchronically, in the vasculature or other body lumen or cavity at atreatment region.

The medical devices and/or medical device components comprising metallicmaterials as described herein can be bio-corrodible. As used herein,“bio-corrodible” means the ability for the metallic portions of amedical device to absorb, resorb, corrode, fracture, dissolve, degrade,and/or disintegrate partially or fully over time while residing inside apatient and when exposed to a physiological environment, which caninclude fluids, electrolytes and dissolved gasses such as hydrogen ions,chloride ions, sodium ions, potassium ions, bicarbonate, phosphate,blood, lymph, proteins, amino acids, plasma, oxygen, carbon dioxide, andthe like. Bio-corrosion may involve any combination of metal corrosionprocesses such as galvanic, pit, crevice, intra-granular,inter-granular, stress-corrosion cracking, corrosion fatigue, frettingcorrosion, and the like. Bio-corrosion may comprise any combination anddegree of uniform and non-uniform disintegration, for example withaccelerated or decelerated zones of corrosion, varying ratios of inter-to intra-grain corrosion, varying degrees of fragmentation of the deviceor elements of the device, and further corrosion of the fragments.

As used herein, “bioabsorbable” means the ability for a medical devicecomprising polymeric components to hydrolyze, corrode, degrade,dissolve, absorb, resorb, or otherwise assimilates into the bodypartially or fully over time while residing inside a patient and whenexposed to a physiological environment, which can include water,electrolytes and dissolved gasses such as hydrogen ions, chloride ions,sodium ions, potassium ions, bicarbonate, phosphate, blood, lymph,proteins, amino acids, plasma, oxygen, carbon dioxide, and the like. Forexample, organic polymers such as polyesters may degrade in vivo bychemical transformations such as hydrolysis.

For example, with reference to FIG. 1, a medical device 100 inaccordance with the present disclosure comprises a graft member 104 anda stent member 102 located about at least the proximal end of graftmember 104. In various embodiments, graft member 104 comprises apolymeric membrane capable of sealing off a section of vessel wall, e.g.sealing perforations and ruptures, and/or correcting abnormalities,e.g., aneurysms, dissections, and fistulas, and/or to protecting asystem from vessel wall lesions, e.g., preventing/minimizing theshedding of materials from lesions (e.g., plaque) into the bloodstream.Stent member 102 can comprise a structural framework that supports graftmember 104 and/or a vessel. Device 100 can have a delivery profileconfigured to traverse a tortuous vasculature and capable of expansionto a nominal diameter. Device 100 can be balloon expandable orself-expanding.

Graft member 104 can comprise an interior and an exterior surface. Invarious embodiments, graft member 104 is configured such that stentmember 102 is disposed on and concentrically surrounds at least aportion of the exterior surface. In such configurations, the interiorsurface of graft member 104 is exposed to the interior of the treatmentarea, such as, for example, a blood vessel. In an embodiment, graftmember 104 can comprise a tubular form having a lumen extending therethrough. In various embodiments, the interior of graft member 104 issufficiently impermeable to a fluid in order to prevent blood frompassing through graft member 104.

In various embodiments, graft member 104 can comprise an exteriorsurface that allows for tissue in-growth. Facilitating in-growth permitsgraft member 104 to be incorporated into the vessel wall after a period.In an embodiment, the exterior surface of graft member 104 can comprisea material that has an open, porous microstructure. An open,microstructure provides an uneven surface topography having crevices,tunnels, and cavernous features within which cells and tissue(s) canoccupy. Similarly, in other embodiments, the exterior surface cancomprise an open macrostructure which can facilitate tissue in growth,e.g., a surface providing a lattice framework that provides an unevensurface topography with surface features within which cells andtissue(s) can occupy. In addition, the outer surface can be coated ortreated with beneficial agents that enhance the rate of tissue ingrowth. For example, in an embodiment, a beneficial agent can comprise apro-angeogenic agent, such as a vascular endothelial growth factor.

In various embodiments, stent member 102 can comprise a structuralsupport that when expanded, does not completely cover graft member 102,leaving it partially exposed in a manner to facilitate tissue in-growth.In other embodiments, stent member 102 contributes a macrostructurehaving an uneven surface topography for in-growth.

Graft member 104 can comprise, for example, expandedpolytetrafluoroethylene (ePTFE), polyester, polyurethane,fluoropolymers, such as perfouorelastomers and the like,polytetrafluoroethylene, silicones, urethanes, ultra high molecularweight polyethylene, aramid fibers, and combinations thereof. Otherembodiments for a graft member material can include high strengthpolymer fibers such as ultra high molecular weight polyethylene fibers(e.g., Spectra®, Dyneema Purity®, etc.), other polyethylenes such asDacron®, or aramid fibers (e.g., Technora®, etc.). Embodiments of ePTFEfor use in a graft are further described in U.S. Pat. No. 5,476,589 toBacino and U.S. Pat. No. 5,814,405 to Branca et al. In an embodiment,graft member 104 can comprise a bioabsorbable organic material, such aspoly(amino acids), poly(anhydrides), and the hydrolysable polyesters,such as poly(caprolactones), poly(lactic/glycolic acid),poly(hydroxybutyrates) and poly(orthoesters). Any graft member that iscapable of providing a lumen for fluid flow within the body of a patientis within the scope of the present disclosure.

In some embodiments, stent member 102 is a structural frameworkconfigured to provide a desired amount of support to hold the lumen ofgraft member 104 radially open within a vessel. The stent member 102needs only to be supportive of graft member 104 long enough until tissuesufficiently in-grows into graft member 102. In an embodiment, stentmember 102 is located along only a portion of graft member 102, such asthe proximal end. In an embodiment, stent member 102 provides sufficientrigidity to the graft member so that it will not radially collapse orotherwise constrict the lumen upon deployment.

Accordingly, in various embodiments, stent member 102 is configured toprovide a threshold level of support to a graft member 104 within a bodylumen, such as a blood vessel for at least a specific period. The periodfor which the stent member 102 is to provide sufficient support to thegraft member 104 can be referred to as a treatment period. The treatmentperiod can correspond with, for example, the estimated time required forsufficient tissue in-growth within the graft member 104 to occur, thusobviating the need for the support provided by stent member 102.

To provide further structural support to the graft member 104, invarious embodiments, the proximal end (in flow side) can have a securingmechanism to seat the proximal end to vessel wall, e.g., an anchor,barb, or other tissue-securing device. The securing mechanism can beconfigured to actuate upon expansion.

In an embodiment, device 100 can be suitable as an intracranialstent-graft. In an embodiment, device 100 can comprise a thin, wispygraft member 104, e.g., a tubular form having a nominal diameter ofbetween about 2 mm to about 6 mm and wall thickness of less than about 6μm to less than about 4 μm. A thin graft member 104 can comprise alightweight structural framework to hold the lumen open in a vessel. Thethickness and/or width of the features making up the stent member 102can be between about 0.1 μm to about 1 mm, or more.

The present disclosure also contemplates stent member 102 can be a morerobust structural framework configured to provide a desired amount ofsupport to dilate a vessel or hold open a vessel. In variousembodiments, stent member 102 is configured to provide a threshold levelof support to a vessel, such as a blood vessel for a period sufficientfor the supported tissue to remodel.

Stent member 102 can comprise a bio-corrodible material. In suchconfigurations, after medical device 100 is deployed in the treatmentarea, stent member 102 begins to bio-corrode. As stent member 102bio-corrodes, the amount of support provided to the graft memberdecreases. Eventually, stent member 102 can bio-corrode such that adesired level of support is no longer provided by stent member 102 tothe treatment area. In embodiments intended to treat cerebral pathologysuch as aneurysms and those devices including a graft material, stentmember 102 and optionally a securing mechanism merely needs to hold thegraft material open and in place long enough for cellular in-growth totake place. In other words, the vessel itself may need no support; it isthe graft member 104 component requiring temporary support to resistacute migration caused by shear forces of blood flow. Once tissuein-growth occurs, the minimal support provided by the stent member 102is no longer required.

In a further embodiment, stent member 102 can be configured tobio-corrode in an approximated predictable manner after deployment tothe treatment area. For example, stent member 102 can comprise abio-corrodible material that bio-corrodes at an approximate predictablerate. In such embodiments, one or more of the pattern of stent member102, material type, and/or its rate of corrosion to provide sufficientstructure to a body lumen, such a blood vessel, for a desired treatmentperiod. For example, physical attributes thickness and width of stentmember features can be selected to provide sufficient support for thetreatment period. In addition, increasing or decreasing the number ofstructural features, such as bands, struts, and/or tessellations, can bevaried. Further tailoring includes, selecting a material that has highstrength properties comparable to that of stainless steel can be used toconstruct a lightweight or delicate framework and yet still providesufficient structural support to graft member. For example, thethickness of stent member 102 can be chosen such that stent member 102provides sufficient support at the treatment area for at least theduration of the treatment period. Other physical attributes of stentmember 102, such as the pattern and/or surface profile of stent member102 can be selected to provide a predictable timeframe for bio-corrosionof stent member 102.

In various embodiments, one or more physical attributes of stent member102 can be selected to provide sufficient support for a treatment periodbut also to account for long-term concerns over an implant present incertain treatment areas. For example, in cerebral suitable embodimentsin, the thickness of stent member 102 can be minimized to preventreducing the cross sectional profile of the vessel. Furthermore, inbio-corrodible embodiments in which a lightweight stent member issufficiently supportive, the thickness of stent member 102 can beminimized to reduce the amount of degradation byproducts.

In various embodiments, the bio-corrodible material comprises abio-corrodible metal or metal alloy. For example, stent member 102 cancomprise iron, magnesium, zinc, tungsten, or an alloy of thereof. Aniron alloy refers to a metal composition with iron (Fe) present as themajor component. In various embodiments, an iron alloy may comprise apercent (by weight) iron concentration within the range of at leastabout 50% to at least about 95%. In addition to the elemental iron, ironalloys for use in stent member 102 can comprise non-iron elements suchas carbon, nickel, cobalt, manganese, magnesium, lithium, calcium,chromium, molybdenum, tantalum, platinum, palladium, vanadium, iridium,rhenium, rhodium, rubidium, osmium, tungsten, titanium, niobium,zirconium, hafnium, aluminum, boron, sulfur, tin, silicon, yttrium,zinc, bismuth, silver, copper, iridium, indium, tin, and any lanthanideor actinide. In various embodiments, an iron alloy for stent member 102can comprise from 0 to about 40% manganese, 0 to about 5% chromium, 0 toabout 10% nickel, 0 to about 25% cobalt, 0 to about 1% aluminum, 0 toabout 5% molybdenum, 0 to about 3% titanium, 0 to about 3% zirconium, 0to about 1% carbon, 0 to about 1% silicon, 0 to about 3% niobium, 0 toabout 1% nitrogen, and 0 to about 1% yttrium, with the remainder iron.Bio-corrodible iron alloys can lack those elements acknowledged as beingbeneficial in enhancing the corrosion resistance of iron, e.g.,chromium, nickel, molybdenum, copper, titanium, vanadium, and silicon.Examples of iron alloys for use in stent member 102 can be found in U.S.Pat. No. 8,246,762 to Janko et al., the content of which is herebyincorporated by reference in its entirety. Notwithstanding the above,stent member 102 can comprise any bio-corrodible metal or metal alloycapable of providing temporary or semi-permanent support to a lumenwithin the body of a patient, such as a blood vessel.

In various embodiments, stent member 102 comprises a layer or pattern ofbio-corrodible metal or metal alloy applied directly to a graft member,such as graft member 104. In various embodiments, the bio-corrodiblemetal or metal alloy can be applied to graft member 104 through a vapordeposition process, an electroless deposition, or other depositionprocess. Deposition technology enables the construction of a lightweightstent member with minimal metal for the desired level of structuralsupport.

During vapor deposition, the process parameters, such as chamberpressure, deposition pressure, partial pressure of the process gases,the target temperature, bias voltage, substrate or source movementrelative to the target, the number and type of substrates, and power arecontrolled to optimize deposition of the desired species onto the graftmember 104. In further embodiments, once the initial layer is vapordeposited, additional layers can optionally be added throughelectroplating.

Alternatively or in addition thereto, a bioabsorbable polymer can bedirectly applied to graft member 104 or overlying stent member 102, alsothrough a deposition process.

In order to construct device through a deposition process, graft member104 can optionally comprise an exterior surface or a portion thereofthat has been treated, coated, and/or constructed to facilitate adhesionof stent member 102 to graft member 104. In an embodiment, the portionof the exterior surface treated, coated, or constructed to facilitateadhesion can form a stent member 104 pattern. For example, the exteriorsurface of graft member 104 can be coated, whether continuously ordiscontinuously, with an adhesive, e.g., a biocompatible hot meltadhesive, in a stent member 102 pattern. A suitable adhesive cancomprise a fluoropolymer adhesive, such as fluorinated ethylenepropylene (FEP). By way of another example, the exterior surface cancomprise an ePTFE layer with an open microstructure that provides asurface topography of varying heights. The uneven topography can be moreamenable to stent member 102 adhesion. In an embodiment, the ePTFEmaterial can comprise a node and fibril structure or substantiallyfibrillated structure. The size of the nodes and fibrils can beengineered to create a desired surface topography. In another example,the exterior surface can comprise inset channels that define the stentmember 102 pattern; as such, the stent member 102 is inset, at leastpartially, into graft member 104.

In various embodiments, graft member 104 can comprise an exteriorsurface or a portion thereof that has been treated, coated, and/orconstructed to provide protection to graft member 104 from degradationduring the deposition process. In other embodiments, graft member 104damage occurring because of a deposition process can result in a moreuneven surface topography that can facilitate cellular in-growth aspreviously described. For example, plasma particles generated during asputter coating process can inadvertently hit the substrate and resultin a more reticulated, uneven surface topography.

In accordance with another aspect of the disclosure, the medical devicecan be delivered endovascularly, and thus, a delivery system cancomprise medical device 100 as described herein mounted at or near thedistal end of a catheter or guidewire about an expansion member and/orconstrained with a constraining device. In an embodiment, expansionmember is a balloon that is inflated at the treatment site to deploymedical device 100.

In an embodiment, the described medical device 100 can be constructed atthe delivery diameter and can be crimped onto balloon. The deliverysystem can be introduced into the vasculature and tracked on a wire tothe treatment site, e.g., at the site of a cerebral lesion. Oncepositioned, the balloon can be distended to a profile, which providesintimate contact with the vessel wall, which can cause the stent member102 to plastically deform. The pressure required for such distension canbe a low pressure in the embodiments where stent member 102 is alightweight structural framework.

With reference to FIG. 2, a method 200 for forming stent member 102directly on the surface of graft member 104 using vapor deposition isillustrated. Method 200 comprises provide graft member step 10. Providegraft member step 10 comprises selecting a graft member suitable bothfor implantation in the anatomy of a patient and for receiving andsupporting a bio-corrodible stent member, such as stent member 102. Thegraft member of step 10 can comprise graft member 104, as describedabove.

Method 200 further comprises a select stent mask step 20. Select maskstep 20 comprises selecting a mask that corresponds with a desiredpattern for stent member 102. The pattern can comprise an open-cell orclosed-cell conformation. The pattern can comprise a series of adjacentbands, e.g., undulating rings, and interconnecting struts and/or atessellated pattern. During use, bands can be expanded from an initial,small diameter to a larger diameter to contact the stent member 102against a wall of a vessel, thereby maintaining the patency of thevessel. Struts can be utilized to vary the degree of stent member 102flexibility and/or conformability that allow the stent member 102 toadapt to the contours of the vessel. With reference to FIGS. 3A-3C,various masks 110 are illustrated. In various embodiments, masks 110comprise a cylinder capable of concentrically surrounding at least aportion of graft member 104. Each mask 110 comprises a pattern 112. Invarious embodiments, pattern 112 comprises the inverse of the desiredstructure of stent member 102. However, any mask capable of forming adesired pattern in a stent member 102 is within the scope of the presentdisclosure. Once selected, mask 110 can be applied to graft member 104such that it concentrically surrounds at least a portion of graft member104.

Method 200 further comprises a deposit stent material step 30. Invarious embodiments, deposit stent material step 30 comprises exposinggraft member 104 to a substrate deposition process. The substratedeposition process can be any process that sufficiently preserves thegraft member's mechanical and chemical performance properties whiledepositing the structural framework to the graft member 104. Depositionprocesses can include sputter deposition, resistive thermal deposition,electron beam evaporation, or other suitable processes.

For example, deposit stent material step 30 comprises exposing themasked graft member 104 to a vapor deposition source. The vapordeposition source contains the bio-corrodible metal or metal alloy thatwill constitute stent member 102. Stent member 102 is formed by thedeposition of the desired bio-corrodible metal or metal alloy on thesurface of graft member 104 exposed by mask 110. The bio-corrodiblemetal is deposited on the surface of graft member 104 over an exposedregion 114 of mask 110. The resulting stent member 102 comprises abio-corrodible metal or metal alloy in the general shape of pattern 112.After stent member 102 has been formed on the surface of graft member104, mask 110 can be removed from graft member 104.

In some embodiments, graft member 104 can be coupled to a mandrel inpreparation for exposure to a vapor deposition source. The mandrel canbe configured to rotate and to be laterally displaced according to adesired pattern. The desired pattern can comprise, for example, ahelical or undulating helical shape. By rotating and/or laterallydisplacing the mandrel and graft member 104 and/or the deposition sourceaccording to the desired pattern, metal or metal alloy from thedeposition source is deposited along the surface of graft member 104 inthe desired pattern. Once completed, graft member 104 and newly formedstent member 102 can be removed from the mandrel and prepared forimplantation in the body of a patient.

In other embodiments, a deposition process can comprise an electrolessdeposition. Graft member can be dipped into a solution wherein metalwill deposit on the catalytically active sites of the graft member. Acatalytic reagent can be applied to the exterior surface of the graftmember in a desired pattern to which the metal components within thesolution will deposit. In an embodiment, an electroless solution cancomprise iron, manganese, niobium, and carbon proportioned to create ahigh percentage manganese, iron alloy.

In various embodiments, post deposition processing, such as annealing,may also be required to obtain a stent member 102 of sufficientductility to maintain structural support. Annealing can be localized tominimize the damaging effects to the graft member 104 that can be causedby increased temperatures.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present disclosurewithout departing from the spirit or scope of the disclosure. Thus, itis intended that the present disclosure cover the modifications andvariations of this disclosure provided they come within the scope of theappended claims and their equivalents.

Likewise, numerous characteristics and advantages have been set forth inthe preceding description, including various alternatives together withdetails of the structure and function of the devices and/or methods. Thedisclosure is intended as illustrative only and as such is not intendedto be exhaustive. It will be evident to those skilled in the art thatvarious modifications can be made, especially in matters of structure,materials, elements, components, shape, size and arrangement of partsincluding combinations within the principles of the disclosure, to thefull extent indicated by the broad, general meaning of the terms inwhich the appended claims are expressed. To the extent that thesevarious modifications do not depart from the spirit and scope of theappended claims, they are intended to be encompassed therein.

What is claimed is:
 1. A method of making a medical device forimplantation in a body of a patient, the method comprising: providing agraft member having a continuous, tubular form; and exposing the graftmember to a bio-corrodible metal in at least one of a vapor depositionprocess or an electroless deposition process to form a stent member onthe surface of the graft member, the graft member comprising an expandedpolytetrafluoroethylene and the stent member providing radial support tothe graft member and formed of a material having a range of 0-5%chromium content, the material of the stent member being chosen to bebio-corrodible following implantation in the patient such that the stentmember provides reduced structural support to the graft member over timefollowing implantation in the body.
 2. The method of claim 1, furthercomprising the steps of providing a deposition mask, and applying thedeposition mask to the graft member.
 3. The method of claim 1, whereinthe bio-corrodible metal comprises iron and magnesium.
 4. The method ofclaim 1 wherein the graft member has a lumen and an outer surface, thestent member being formed on the outer surface of the graft member.
 5. Amethod of making a medical device for implantation in a body of apatient, the method comprising: providing a graft member having acontinuous, tubular form; and exposing the graft member to abio-corrodible metal in at least one of a vapor deposition process or anelectroless deposition process to form a stent member on the surface ofthe graft member, the graft member comprising a bioabsorbable polymerand the stent member providing radial support to the graft member andformed of a material having a range of 0-5% chromium content, thematerial of the stent member being chosen to be bio-corrodible followingimplantation in the patient such that the stent member provides reducedstructural support to the graft member over time following implantationin the body.
 6. The method of claim 1, further comprising the steps ofproviding a deposition mask, and applying the deposition mask to thegraft member.
 7. The method of claim 1, wherein the bio-corrodible metalcomprises iron and magnesium.
 8. The method of claim 5 wherein the graftmember has a lumen and an outer surface, the stent member being formedon the outer surface of the graft member.